Identification of CuO Species in High Surface Area CuO−CeO2Catalysts and Their Catalytic Activities for CO Oxidation

Nanosized CuO−CeO 2 catalysts with high surface area (>90 m 2 g -1 ) were prepared by a modified citrate sol−gel method with incorporation of N 2 thermal treatment. CO temperature-programmed reduction results indicated that there are three CuO species in the catalyst, namely, the finely dispersed CuO, the bulk CuO, and the Cu 2+ in the CeO 2 lattice. Using CO oxidation as a model reaction, catalytic activity of each species was evaluated. It was found that the finely dispersed CuO species had the highest activity (183.3 mmol CO g Cu -1 h -1 ) and the bulk CuO had medium activity (100.4 mmol CO g Cu -1 h -1 ), while the Cu 2+ in the CeO 2 lattice had the lowest activity (21.3 mmol CO g Cu -1 h -1 ). Furthermore, the Cu 2+ species in the CeO 2 lattice could migrate to the catalyst surface to form finely dispersed CuO under high-temperature calcination or under reaction conditions, which could consequently enhance the catalytic activity.